Fuel cell system and method of operating a fuel cell system

Abstract

A fuel cell system includes a fuel cell having an anode region and a cathode region. The fuel cell defines an anode inlet to permit feeding the anode region with hydrogen and defines a cathode inlet to permit feeding the cathode region with oxygen. The fuel cell has an anode outlet and has a cathode outlet. An anode outlet conduit receives anode offgas at the anode outlet and a catalytic converter is arranged so as to permit the anode offgas in the anode outlet conduit to flow therethrough. A cathode outlet conduit is arranged for receiving cathode offgas at the cathode outlet. A cathode branch conduit connects the cathode outlet conduit to the anode outlet conduit upstream of the catalytic converter.

1 . A fuel cell system comprising:
 a fuel cell having an anode region and a cathode region;   said fuel cell defining an anode inlet to permit feeding said anode region with hydrogen;   said fuel cell defining a cathode inlet to permit feeding said cathode region with oxygen;   said fuel cell having an anode outlet and having a cathode outlet;   an anode outlet conduit for receiving anode offgas at said anode outlet;   a catalytic converter arranged so as to permit said anode offgas in said anode outlet conduit to flow therethrough;   a cathode outlet conduit arranged for receiving cathode offgas at said cathode outlet; and,   a cathode branch conduit connecting said cathode outlet conduit to said anode outlet conduit upstream of said catalytic converter.   
     
     
         2 . The fuel cell system of  claim 1 , further comprising: a flow-directing unit assigned to said cathode branch conduit for directing a first portion of said cathode offgas into said cathode branch conduit thereby leaving a remainder portion of said cathode offgas not branched off from said cathode outlet conduit. 
     
     
         3 . The fuel cell system of  claim 2 , wherein the portion of said cathode offgas introduced into said cathode branch conduit is variable via said flow-directing unit. 
     
     
         4 . The fuel cell system of  claim 1 , further comprising:
 a cathode offgas demoisturizing unit arranged in accordance with at least one of the following:   i) in said cathode outlet conduit upstream of a branch of said cathode branch conduit from said cathode outlet conduit; and,   ii) in said cathode branch conduit.   
     
     
         5 . The fuel cell system of  claim 2 , further comprising: a fuel cell offgas system for receiving said remainder portion of said cathode offgas and for receiving a mixture of said anode offgas with said first portion of said cathode offgas with said mixture having been released from said catalytic converter after performance of a catalytic reaction. 
     
     
         6 . The fuel cell system of  claim 5 , wherein said fuel cell offgas system includes a demoisturizing unit or/and a muffler. 
     
     
         7 . The fuel cell system of  claim 1 , wherein said fuel cell system is for a vehicle. 
     
     
         8 . A method of operating a fuel cell system including: a fuel cell having an anode region and a cathode region; said fuel cell defining an anode inlet to permit feeding said anode region with hydrogen; said fuel cell defining a cathode inlet to permit feeding said cathode region with oxygen; said fuel cell having an anode outlet and having a cathode outlet; an anode outlet conduit for receiving anode offgas at said anode outlet; a catalytic converter arranged so as to permit said anode offgas in said anode outlet conduit to flow therethrough; a cathode outlet conduit arranged for receiving cathode offgas at said cathode outlet; and, a cathode branch conduit connecting said cathode outlet conduit to said anode outlet conduit upstream of said catalytic converter, the method comprising:
 directing said anode offgas released at said anode outlet of said fuel cell through said catalytic converter to reduce the hydrogen content in said anode offgas; and,   adding a portion of said cathode offgas released at said cathode outlet to said anode offgas upstream of said catalytic converter.   
     
     
         9 . The method of  claim 8 , wherein the portion of the cathode offgas added to the anode offgas is variable. 
     
     
         10 . The method of  claim 9 , wherein the amount of the cathode offgas added to the anode offgas is adjusted depending on the hydrogen content in the anode offgas released at the anode outlet. 
     
     
         11 . The method of  claim 9 , wherein the amount of the cathode offgas added to the anode offgas is adjusted such that an at least stoichiometric oxygen/hydrogen ratio is provided for catalytic reaction in said catalytic converter. 
     
     
         12 . The method of  claim 9 , wherein the amount of the cathode offgas added to the anode offgas is adjusted such that an at least superstoichiometric oxygen/hydrogen ratio is provided for catalytic reaction in said catalytic converter. 
     
     
         13 . The method of  claim 11 , wherein the amount of the cathode offgas added to the anode offgas is adjusted such that the mixture of anode offgas and cathode offgas supplied to said catalytic converter has a hydrogen content below a threshold hydrogen content. 
     
     
         14 . The method of  claim 13 , wherein the threshold hydrogen content lies in a range from 4% by volume to 8% by volume. 
     
     
         15 . The method of  claim 8 , wherein the portion of the cathode offgas not added to the anode offgas and the mixture of the anode offgas and of the portion of the cathode offgas added to the anode offgas that leaves said catalytic converter after performance of the catalytic reaction are directed into a fuel cell offgas system. 
     
     
         16 . The method of  claim 8 , wherein said fuel cell system is for a vehicle.